While solar photovoltaic (PV) systems dominate the renewable energy landscape, solar thermal technology offers a complementary and promising avenue for decarbonization. In India, where solar resources are abundant, solar thermal technologies can play a pivotal role in reducing greenhouse gas emissions and meeting the growing energy demands sustainably.

 

Current Scenario

India has been leveraging solar thermal technologies for various applications, from domestic solar water heaters to large-scale solar thermal power plants. As of 2023, India has an estimated installed capacity of around 6.8 million square meters of solar water heating systems. Concentrated Solar Power (CSP) projects, though less prevalent, are emerging as a potential high-impact technology with projects like the 100 MW Rajasthan Sun Technique CSP plant.

Key Technology

Domestic and Industrial Heating

• Solar Water Heaters: As of 2023, India has approximately 6.8 million square meters of installed solar water heaters, with an estimated annual energy saving of about 1,100 million kWh, which equates to a reduction of around 1 million tons of CO2 emissions.
• Industrial Heating Applications: In industries like food processing and textiles, solar thermal systems can provide temperatures up to 100°C. For example, a textile factory in Tamil Nadu uses a solar thermal system to generate steam, reducing its annual coal consumption by 300 tons and CO2 emissions by approximately 750 tons.

High-Temperature Applications

• Concentrated Solar Power (CSP): CSP systems can achieve temperatures above 500°C, suitable for high-temperature industrial processes. The Rajasthan Sun Technique CSP plant generates 100 MW, contributing to the grid and offsetting about 250,000 tons of CO2 annually.
• Solar Industrial Process Heat: The National Solar Mission includes initiatives to deploy solar thermal technologies for industrial process heat. A pilot project in Gujarat using solar concentrators provides 150°C steam for a dairy plant, saving approximately 1,200 liters of diesel per day and reducing CO2 emissions by 1,800 tons per year.

Energy Storage

• Thermal Energy Storage (TES): CSP plants with TES can store energy for use during non-sunny periods. For instance, the planned CSP plant in Rajasthan will use molten salt storage to provide 6 hours of thermal storage, ensuring a stable supply of 50 MW power, even during cloudy periods or after sunset.
• Cost-Effectiveness: Storing thermal energy is generally cheaper and more efficient than electrical energy storage. TES systems in CSP plants can achieve storage costs of $20-30 per kWh, compared to $200-300 per kWh for battery storage systems.

Hybrid Systems

• Solar PV and CSP Hybrid Plants: Combining PV and CSP can optimize energy production and storage. A hybrid project in Gujarat integrates 25 MW of PV with 50 MW of CSP and 6 hours of thermal storage, demonstrating a reduction in reliance on fossil fuels and improved grid stability.
• Solar-Biomass Hybrid Systems: A pilot project in Maharashtra combines solar thermal with biomass to provide continuous heat for a food processing unit, reducing annual diesel consumption by 80,000 liters and CO2 emissions by 200 tons.

Advanced Materials and Coatings

• High-Reflectivity Mirrors: New mirror technologies with reflectivity rates exceeding 95% are being tested. These mirrors can significantly enhance the efficiency of CSP systems by reducing energy losses. The National Institute of Solar Energy (NISE) in India is conducting trials on these advanced mirrors.
• Heat Transfer Fluids: Innovations in heat transfer fluids, such as nanofluids, are improving the thermal conductivity and stability of CSP systems. Research at IIT Bombay has shown that nanofluids can increase heat transfer rates by up to 20%, enhancing overall system performance.

Case Studies

• Rajasthan Sun Technique CSP Plant: This 100 MW plant, using parabolic trough technology, demonstrates the potential of CSP in India. Innovations in this plant include advanced heat transfer fluids and high-efficiency reflectors, contributing to its success.
• Solar Water Heating in Bangalore: Bangalore's widespread adoption of solar water heaters has led to significant electricity savings. The city’s policy mandates solar water heaters for new buildings, resulting in an estimated reduction of 200 GWh in annual electricity consumption.
• National Solar Mission Projects: Under the Jawaharlal Nehru National Solar Mission, several pilot projects have been initiated to test advanced solar thermal technologies. For instance, a project in Rajasthan is piloting a CSP plant with integrated molten salt storage, aiming to provide a 24/7 power supply.